Polyimide films and electronic devices

ABSTRACT

In a first aspect, a polyimide film includes a polyimide derived from a dianhydride and a diamine. The dianhydride includes pyromellitic dianhydride, the diamine includes a benzimidazole, the molar ratio of dianhydride to diamine that forms the polyimide is in a range of from 0.85:1 to 0.99:1, and the polyimide film has a Tg of 400° C. or higher, a tensile modulus of 6.0 GPa or more, and a coefficient of thermal expansion of 15 ppm/° C. or less over a temperature range of 50 to 500° C. In a second aspect, an electronic device includes the polyimide film of the first aspect.

FIELD OF DISCLOSURE

The field of this disclosure is polyimide films, electronic devices andpolyamic acid solutions.

BACKGROUND OF THE DISCLOSURE

Polymer films having high temperature stability, high tensile modulusand low coefficient of thermal expansion (CTE) are needed for flexibledisplay applications, such as for thin-film transistor (TFT) substratesin organic light-emitting diode (OLED) displays, electronic paper(E-paper) and touch sensor panels (TSPs) for displays. For example,aromatic polyimides are typically very thermally stable, with glasstransition temperatures (T_(g)) of greater than 320° C., and haveexcellent foldability and rollability, making them ideal candidates foruse in various layers of flexible display devices, such as touch sensorpanels and cover windows. But for flexible TFT substrates, in additionto good bending properties, TFT manufacturing processes require filmsthat are stable at temperatures of 400° C. or higher for extendedperiods of time, while also having low CTE's and maintaining hightensile moduli.

Polymer fibers containing benzimidazole can exhibit high strength, highglass transition temperature (T_(g)), and low CTE due to theintroduction of intramolecular hydrogen-bonding in the main polymerchain, forming highly oriented, well-ordered dense-packing molecularstructures in the fiber. Polybenzimidazole (PBI) is an extremely heatresistant heterocyclic polymer. With a T_(g) of about 430° C., it showssuperior dimensional stability, retention of stiffness and toughness attemperatures over 400° C. and has been widely used in theaerospace/defense industry, in fire-fighting equipment, and as themembrane in fuel cells in the form of fiber or resin. PBI also has ahigher modulus and is stronger than typical polyimides. Polyimide filmscontaining a benzimidazole-based diamine, such as5-amino-2-(4-aminophenyl)benzimidazole (DAPBI), can possess outstandingthermal and oxidative stability under extreme conditions whilemaintaining good mechanical properties. However, the stronghydrogen-bonding interaction introduced by benzimidazoles can alsopresent challenges in processing polyamic acid solutions used to makepolyimide films. For example, a robust roll-to-roll film-making processfor polyimide films requires good control of the viscosity and solidscontent of the liquid polyamic acid solutions to enable a commerciallysustainable process. U.S. Pat. No. 6,770,733 B2 describes afilm-formable polyimide copolymer having a benzimidazole, where thedianhydride used for the polyimide is a combination of pyromelliticdianhydride (PMDA) and 3,3′,4,4′-benzophenone tetracarboxylic aciddianhydride (BTDA). When trying to use PMDA, without any BTDA, as thesole dianhydride for the polymer, however, it is not possible to form afilm. A similar effort to make robust polyimide films (S. Wang et al.,J. Polym. Sci. Polym. Chem. (2009), 47(8), 2024-2031) shows that usingonly PMDA and DAPBI as the dianhydride and diamine monomers isproblematic due to the rigid nature of the polymer backbone. More recentefforts to make PMDA//DAPBI polyimide films (Chinese Patent ApplicationPublication No. CN106928481 A and Japanese Patent ApplicationPublication No. JP2018-104525 A) describe processes to carefully handlelow solids, low viscosity polyamic acid solutions to make polyimidefilms that have high T_(g) (>400° C.), but these polyimide films arefragile and brittle, preventing the inventors from performing mechanicaltests on these samples.

There remains a need for robust polymer films with high T_(g), low CTEand high tensile modulus that can be used in flexible deviceapplications.

SUMMARY

In a first aspect, a polyimide film includes a polyimide derived from adianhydride and a diamine. The dianhydride includes pyromelliticdianhydride, the diamine includes a benzimidazole, the molar ratio ofdianhydride to diamine that forms the polyimide is in a range of from0.85:1 to 0.99:1, and the polyimide film has a T_(g) of 400° C. orhigher, a tensile modulus of 6.0 GPa or more, and a coefficient ofthermal expansion of 15 ppm/° C. or less over a temperature range of 50to 500° C.

In a second aspect, an electronic device includes the polyimide film ofthe first aspect.

In a third aspect, a polyamic acid solution includes a dianhydride and adiamine. The dianhydride includes pyromellitic dianhydride, the diamineincludes a benzimidazole, the molar ratio of dianhydride monomer todiamine monomer is in a range of from 0.85:1 to 0.99:1, and the polyamicacid solution has a solids content in a range of from 10 to 25 weightpercent and a viscosity in a range of from 300 to 3000 poise.

The foregoing general description and the following detailed descriptionare exemplary and explanatory only and are not restrictive of theinvention, as defined in the appended claims.

DETAILED DESCRIPTION

In a first aspect, a polyimide film includes a polyimide derived from adianhydride and a diamine. The dianhydride includes pyromelliticdianhydride, the diamine includes a benzimidazole, the molar ratio ofdianhydride to diamine that forms the polyimide is in a range of from0.85:1 to 0.99:1, and the polyimide film has a T_(g) of 400° C. orhigher, a tensile modulus of 6.0 GPa or more, and a coefficient ofthermal expansion of 15 ppm/° C. or less over a temperature range of 50to 500° C.

In one embodiment of the first aspect, the dianhydride further includesup to 70 mole percent of 3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride, or a mixture thereof,based on the total dianhydride content of the polyimide.

In another embodiment of the first aspect, the benzimidazole is selectedfrom the group consisting of 5-amino-2-(4-aminophenyl)benzimidazole,5-amino-2-(3-aminophenyl)benzimidazole,6,6′-bis[2-(4-aminobenzene)benzimidazole],[2,2′-bi-1H-benzimidazole]-6,6′-diamine and mixtures thereof.

In yet another embodiment of the first aspect, the diamine furtherincludes a benzoxazole. In a specific embodiment, the benzoxazole isselected from the group consisting of5-amino-2-(4-aminophenyl)benzoxazole,2,2′-p-phenylenebis[5-aminobenzoxazole],[2,2′-bibenzoxazole]-5,5′-diamine, 2,6-(4,4′-aminophenyl)benzobisoxazoleand mixtures thereof.

In still another embodiment of the first aspect, the diamine furtherincludes up to 50 mole percent of p-phenylenediamine,m-phenylenediamine, m-tolidine, or a mixture thereof, based on the totaldiamine content of the polyimide.

In still yet another embodiment of the first aspect, the polyimide filmfurther includes a crosslinking agent, a colorant, a matting agent,submicron particles or a mixture thereof.

In a further embodiment of the first aspect, the polyimide film has athickness in a range of from 4 to 150 μm.

In a second aspect, an electronic device includes the polyimide film ofthe first aspect. In a specific embodiment, the polyimide film is usedin device components selected from the group consisting of thin-filmtransistor substrates, substrates for color filter sheets, cover filmsand metal-clad laminates.

In a third aspect, a polyamic acid solution includes a dianhydride and adiamine. The dianhydride includes pyromellitic dianhydride, the diamineincludes a benzimidazole, the molar ratio of dianhydride monomer todiamine monomer is in a range of from 0.85:1 to 0.99:1, and the polyamicacid solution has a solids content in a range of from 10 to 25 weightpercent and a viscosity in a range of from 300 to 3000 poise.

In one embodiment of the third aspect, the dianhydride further includesup to 70 mole percent of 3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride, or a mixture thereof,based on the total dianhydride content of the polyimide.

In another embodiment of the third aspect, the benzimidazole is selectedfrom the group consisting of 5-amino-2-(4-aminophenyl)benzimidazole,5-amino-2-(3-aminophenyl)benzimidazole,6,6′-bis[2-(4-aminobenzene)benzimidazole],[2,2′-bi-1H-benzimidazole]-6,6′-diamine and mixtures thereof.

In yet another embodiment of the third aspect, the diamine furtherincludes a benzoxazole. In a specific embodiment, the benzoxazole isselected from the group consisting of5-amino-2-(4-aminophenyl)benzoxazole,2,2′-p-phenylenebis[5-aminobenzoxazole],[2,2′-bibenzoxazole]-5,5′-diamine, 2,6-(4,4′-aminophenyl)benzobisoxazoleand mixtures thereof.

In still another embodiment of the third aspect, the diamine furtherincludes up to 50 mole percent of p-phenylenediamine,m-phenylenediamine, m-tolidine, or a mixture thereof, based on the totaldiamine content of the polyimide.

In still yet another embodiment of the third aspect, the polyamic acidsolution further includes a crosslinking agent, a colorant, a mattingagent, submicron particles or a mixture thereof.

Many aspects and embodiments have been described above and are merelyexemplary and not limiting. After reading this specification, skilledartisans appreciate that other aspects and embodiments are possiblewithout departing from the scope of the invention. Other features andadvantages of the invention will be apparent from the following detaileddescription, and from the claims.

In one embodiment, a polyamic acid (PAA) solution having bothpyromellitic dianhydride and a benzimidazole-based diamine can be usedto form a polyimide film with a high T_(g), a low CTE and a high tensilemodulus. The PAA solution can have a high solids content and highviscosity. By adjusting the molecular ratio of the dianhydride todiamine monomers in the PAA, good control over the film-forming processenables the production of robust polyimide films, making it possible touse roll-to-roll processing to form continuous, free-standing polyimidefilm. In one embodiment, the PAA solution can be cast on copper foil toform copper-clad laminates. In one embodiment, the polyimide film has aT_(g) of 400° C. or higher, a tensile modulus of 6.0 GPa or more, and acoefficient of thermal expansion of 15 ppm/° C. or less over atemperature range of 50 to 500° C. In one embodiment, the polyamic acidsolution has a solids content in a range of from 10 to 25 wt % and aviscosity in a range of from 300 to 3000 poise. In one embodiment, themolar ratio of dianhydride monomer to diamine monomer is in a range offrom 0.85:1 to 0.99:1. These flexible polyimide films can be used fornumerous applications in the electronics industry where the benefits oftheir high T_(g) (glass transition temperature), high tensile modulusand low CTE (the coefficient of thermal expansion) are desired, such asfor TFT substrates and E-paper, as well as in the manufacture offlexible circuits and copper clad laminates, and in display devices,such as for cover windows, touch sensor panels and other electronicdevice layers.

Depending upon context, “diamine” as used herein is intended to mean:(i) the unreacted form (i.e., a diamine monomer); (ii) a partiallyreacted form (i.e., the portion or portions of an oligomer or otherpolymer precursor derived from or otherwise attributable to diaminemonomer) or (iii) a fully reacted form (the portion or portions of thepolymer derived from or otherwise attributable to diamine monomer). Thediamine can be functionalized with one or more moieties, depending uponthe particular embodiment selected in the practice of the presentinvention.

Indeed, the term “diamine” is not intended to be limiting (orinterpreted literally) as to the number of amine moieties in the diaminecomponent. For example, (ii) and (iii) above include polymeric materialsthat may have two, one, or zero amine moieties. Alternatively, thediamine may be functionalized with additional amine moieties (inaddition to the amine moieties at the ends of the monomer that reactwith dianhydride to propagate a polymeric chain). Such additional aminemoieties could be used to crosslink the polymer or to provide otherfunctionality to the polymer.

Similarly, the term “dianhydride” as used herein is intended to mean thecomponent that reacts with (is complimentary to) the diamine and incombination is capable of reacting to form an intermediate (which canthen be cured into a polymer). Depending upon context, “anhydride” asused herein can mean not only an anhydride moiety per se, but also aprecursor to an anhydride moiety, such as: (i) a pair of carboxylic acidgroups (which can be converted to anhydride by a de-watering orsimilar-type reaction); or (ii) an acid halide (e.g., chloride) esterfunctionality (or any other functionality presently known or developedin the future which is) capable of conversion to anhydridefunctionality.

Depending upon context, “dianhydride” can mean: (i) the unreacted form(i.e. a dianhydride monomer, whether the anhydride functionality is in atrue anhydride form or a precursor anhydride form, as discussed in theprior above paragraph); (ii) a partially reacted form (i.e., the portionor portions of an oligomer or other partially reacted or precursorpolymer composition reacted from or otherwise attributable todianhydride monomer) or (iii) a fully reacted form (the portion orportions of the polymer derived from or otherwise attributable todianhydride monomer).

The dianhydride can be functionalized with one or more moieties,depending upon the particular embodiment selected in the practice of thepresent invention. Indeed, the term “dianhydride” is not intended to belimiting (or interpreted literally) as to the number of anhydridemoieties in the dianhydride component. For example, (i), (ii) and (iii)(in the paragraph above) include organic substances that may have two,one, or zero anhydride moieties, depending upon whether the anhydride isin a precursor state or a reacted state. Alternatively, the dianhydridecomponent may be functionalized with additional anhydride type moieties(in addition to the anhydride moieties that react with diamine toprovide a polymer). Such additional anhydride moieties could be used tocrosslink the polymer or to provide other functionality to the polymer.

Although methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the present invention,suitable methods and materials are described herein.

When an amount, concentration, or other value or parameter is given aseither a range, preferred range or a list of upper preferable values andlower preferable values, this is to be understood as specificallydisclosing all ranges formed from any pair of any upper range limit orpreferred value and any lower range limit or preferred value, regardlessof whether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

In describing certain polymers, it should be understood that sometimesapplicants are referring to the polymers by the monomers used to makethem or the amounts of the monomers used to make them. While such adescription may not include the specific nomenclature used to describethe final polymer or may not contain product-by-process terminology, anysuch reference to monomers and amounts should be interpreted to meanthat the polymer is made from those monomers or that amount of themonomers, and the corresponding polymers and compositions thereof.

The materials, methods, and examples herein are illustrative only and,except as specifically stated, are not intended to be limiting. As usedherein, the terms “comprises,” “comprising,” “includes,” “including,”“has,” “having” or any other variation thereof, are intended to cover anon-exclusive inclusion. For example, a method, process, article, orapparatus that comprises a list of elements is not necessarily limitedonly those elements but may include other elements not expressly listedor inherent to such method, process, article, or apparatus. Further,unless expressly stated to the contrary, “or” refers to an inclusive orand not to an exclusive or. For example, a condition A or B is satisfiedby any one of the following: A is true (or present) and B is false (ornot present), A is false (or not present) and B is true (or present),and both A and B are true (or present).

Also, use of the “a” or “an” are employed to describe elements andcomponents of the invention. This is done merely for convenience and togive a general sense of the invention. This description should be readto include one or at least one and the singular also includes the pluralunless it is obvious that it is meant otherwise.

Organic Solvents

Useful organic solvents for the synthesis of the polymers of the presentinvention are preferably capable of dissolving the polymer precursormaterials. Such a solvent should also have a relatively low boilingpoint, such as below 225° C., so the polymer can be dried at moderate(i.e., more convenient and less costly) temperatures. A boiling point ofless than 210, 205, 200, 195, 190, or 180° C. is preferred.

Useful organic solvents include: N-methylpyrrolidone (NMP),dimethylacetamide (DMAc), methyl ethyl ketone (MEK),N,N′-dimethyl-formamide (DMF), dimethyl sulfoxide (DMSO), tetramethylurea (TMU), glycol ethyl ether, diethyleneglycol diethyl ether,1,2-dimethoxyethane (monoglyme), diethylene glycol dimethyl ether(diglyme), 1,2-bis-(2-methoxyethoxy) ethane (triglyme),gamma-butyrolactone, and bis-(2-methoxyethyl) ether, tetrahydrofuran(THF), ethyl acetate, hydroxyethyl acetate glycol monoacetate, acetoneand mixtures thereof. In one embodiment, preferred solvents includeN-methylpyrrolidone (NMP) and dimethylacetamide (DMAc).

Diamines

In one embodiment a suitable diamine for forming the polyimide filmincludes a benzimidazole. Examples of suitable benzimidazoles include5-amino-2-(4-aminophenyl)benzimidazole (DAPBI),5-amino-2-(3-aminophenyl)benzimidazole (i-DAPBI),6,6′-bis[2-(4-aminobenzene)benzimidazole] and[2,2′-bi-1H-benzimidazole]-6,6′-diamine. In one embodiment the suitablediamine further includes a benzoxazole, such as5-amino-2-(4-aminophenyl)benzoxazole (DAPBO),2,2′-p-phenylenebis[5-aminobenzoxazole],[2,2′-bibenzoxazole]-5,5′-diamine and2,6-(4,4′-aminophenyl)benzobisoxazole.

In one embodiment, up to 50 mole percent of one or more additionaldiamines (based on the total diamine content of the polyamic acidsolution or polyimide) can also be used.

In one embodiment, a suitable additional diamine for forming thepolyimide film can include an aliphatic diamine, such as1,2-diaminoethane, 1,6-diaminohexane, 1,4-diaminobutane, 1,5diaminopentane, 1,7-diaminoheptane, 1,8-diaminooctane,1,9-diaminononane, 1,10-diaminodecane (DMD), 1,11-diaminoundecane,1,12-diaminododecane (DDD), 1,16-hexadecamethylenediamine,1,3-bis(3-aminopropyl)-tetramethyldisiloxane, and combinations thereof.Other aliphatic diamines suitable for practicing the invention includethose having six to twelve carbon atoms or a combination of longer chainand shorter chain diamines so long as both developability andflexibility are maintained. Long chain aliphatic diamines may increaseflexibility.

In one embodiment, a suitable additional diamine for forming thepolyimide film can include an alicyclic diamine (can be fully orpartially saturated), such as a cyclobutane diamine (e.g., cis- andtrans-1,3-diaminocyclobutane, 6-amino-3-azaspiro[3.3]heptane, and3,6-diaminospiro[3.3]heptane), bicyclo[2.2.1]heptane-1,4-diamine,isophoronediamine, and bicyclo[2.2.2]octane-1,4 diamine. Other alicyclicdiamines can include cis-1,4 cyclohexane diamine, trans-1,4 cyclohexanediamine, 1,4-bis(aminomethyl)cyclohexane,4,4′-methylenebis(cyclohexylamine),4,4′-methylenebis(2-methyl-cyclohexylamine), bis(aminomethyl)norbornane.

In one embodiment, a suitable additional diamine for forming thepolyimide film can further include a fluorinated aromatic diamine, suchas 2,2′-bis(trifluoromethyl) benzidine (TFMB),trifluoromethyl-2,4-diaminobenzene, trifluoromethyl-3,5-diaminobenzene,2,2′-bis-(4-aminophenyl)-hexafluoro propane,4,4′-diamino-2,2′-trifluoromethyl diphenyloxide,3,3′-diamino-5,5′-trifluoromethyl diphenyloxide,9.9′-bis(4-aminophenyl)fluorene,4,4′-trifluoromethyl-2,2′-diaminobiphenyl,4,4′-oxy-bis-[2-trifluoromethyl)benzene amine] (1,2,4-OBABTF),4,4′-oxy-bis-[3-trifluoromethyl)benzene amine],4,4′-thio-bis-[(2-trifluoromethyl)benzene-amine],4,4′-thiobis[(3-trifluoromethyl)benzene amine],4,4′-sulfoxyl-bis-[(2-trifluoromethyl)benzene amine,4,4′-sulfoxyl-bis-[(3-trifluoromethyl)benzene amine],4,4′-keto-bis-[(2-trifluoromethyl)benzene amine],1,1-bis[4′-(4″-amino-2″-trifluoromethylphenoxy)phenyl]cyclopentane,1,1-bis[4′-(4″-amino-2″-trifluoromethylphenoxy)phenyl]cyclohexane,2-trifluoromethyl-4,4′-diaminodiphenyl ether;1,4-(2′-trifluoromethyl-4′,4″-diaminodiphenoxy)-benzene,1,4-bis(4′-aminophenoxy)-2-[(3′,5′-ditrifluoromethyl)phenyl]benzene,1,4-bis[2′-cyano-3′(“4-aminophenoxy)phenoxy]-2-[(3′,5′-ditrifluoro-methyl)phenyl]benzene(6FC-diamine),3,5-diamino-4-methyl-2′,3′,5′,6′-tetrafluoro-4′-tri-fluoromethyldiphenyloxide,2,2-Bis[4′(4″-aminophenoxy)phenyl]phthalein-3′,5′-bis(trifluoromethyl)anilide(6FADAP) and 3,3′,5,5′-tetrafluoro-4,4′-diamino-diphenylmethane (TFDAM).In a specific embodiment, the fluorinated diamine is2,2′-bis(trifluoromethyl) benzidine (TFMB).

In one embodiment, any number of additional diamines can be used informing the polyimide film, including p-phenylenediamine (PPD),m-phenylenediamine (MPD), m-tolidine (m-TB),2,5-dimethyl-1,4-diaminobenzene, 2,5-dimethyl-1,4-phenylenediamine(DPX), 2,2-bis-(4-aminophenyl) propane, 1,4-naphthalenediamine,1,5-naphthalenediamine, 4,4′-diaminobiphenyl, 4,4′-diamino terphenyl,4,4′-diamino benzanilide, 4,4′-diaminophenyl benzoate,4,4′-diaminobenzophenone, 4,4′-diaminodiphenylmethane (MDA),4,4′-diaminodiphenyl sulfide, 4,4′-diaminodiphenyl sulfone,3,3′-diaminodiphenyl sulfone, bis-(4-(4-aminophenoxy)phenyl sulfone(BAPS), 4,4′-bis-(aminophenoxy)biphenyl (BAPB), 4,4′-diaminodiphenylether (ODA), 3,4′-diaminodiphenyl ether, 4,4′-diaminobenzophenone,4,4′-isopropylidenedianiline, 2,2′-bis-(3-aminophenyl)propane,N,N-bis-(4-aminophenyl)-n-butylamine, N,N-bis-(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, 3,3′-dimethyl-4,4′-diaminobiphenyl,m-amino benzoyl-p-amino anilide, 4-aminophenyl-3-aminobenzoate,N,N-bis-(4-aminophenyl) aniline, 2,4-diaminotoluene, 2,5-diaminotoluene,2,6-diaminotoluene, 2,4-diamine-5-chlorotoluene,2,4-diamine-6-chlorotoluene, 2,4-bis-(beta-amino-t-butyl) toluene,bis-(p-beta-amino-t-butyl phenyl) ether,p-bis-2-(2-methyl-4-aminopentyl) benzene, m-xylylene diamine, andp-xylylene diamine.

Other useful diamines include 1,2-bis-(4-aminophenoxy)benzene,1,3-bis-(4-aminophenoxy) benzene, 1,2-bis-(3-aminophenoxy)benzene,1,3-bis-(3-aminophenoxy) benzene, 1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene, 1,4-bis-(4-aminophenoxy) benzene, 1,4-bis-(3-aminophenoxy)benzene, 1-(4-aminophenoxy)-4-(3-aminophenoxy) benzene,2,2-bis-(4-[4-aminophenoxy]phenyl) propane (BAPP), 2,2′-bis-(4-phenoxyaniline) isopropylidene, 2,4,6-trimethyl-1,3-diaminobenzene and2,4,6-trimethyl-1,3-diaminobenzene.

Dianhydrides

In one embodiment, a suitable dianhydride for forming the polyimide filmincludes pyromellitic dianhydride (PMDA). In one embodiment, up to 70mole percent of one or more additional dianhydrides (based on the totaldianhydride content of the polyamic acid solution or polyimide) can alsobe used. For instance, any number of suitable additional dianhydridescan be used in forming the polyimide film. The dianhydrides can be usedin their tetra-acid form (or as mono, di, tri, or tetra esters of thetetra acid), or as their diester acid halides (chlorides). However, insome embodiments, the dianhydride form can be preferred, because it isgenerally more reactive than the acid or the ester.

Examples of suitable additional dianhydrides include3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA),2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA),2,2′,3,3′-biphenyltetracarboxylicdianhydride (i-BPDA),1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylicdianhydride, 2-(3′,4′-dicarboxyphenyl) 5,6-dicarboxybenzimidazoledianhydride, 2-(3′,4′-dicarboxyphenyl) 5,6-dicarboxybenzoxazoledianhydride, 2-(3′,4′-dicarboxyphenyl) 5,6-dicarboxybenzothiazoledianhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA),2,2′,3,3′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride,bicyclo-[2,2,2]-octen-(7)-2,3,5,6-tetracarboxylic-2,3,5,6-dianhydride,4,4′-thio-diphthalic anhydride, bis (3,4-dicarboxyphenyl) sulfonedianhydride, bis (3,4-dicarboxyphenyl) sulfoxide dianhydride (DSDA), bis(3,4-dicarboxyphenyl oxadiazole-1,3,4) p-phenylene dianhydride, bis(3,4-dicarboxyphenyl) 2,5-oxadiazole 1,3,4-dianhydride, bis2,5-(3′,4′-dicarboxydiphenylether) 1,3,4-oxadiazole dianhydride,4,4′-oxydiphthalic anhydride (ODPA), bis (3,4-dicarboxyphenyl) thioether dianhydride, bisphenol A dianhydride (BPADA), bisphenol Sdianhydride, bis-1,3-isobenzofurandione, 1,4-bis(4,4′-oxyphthalicanhydride) benzene, bis (3,4-dicarboxyphenyl) methane dianhydride,cyclopentadienyl tetracarboxylic dianhydride, ethylene tetracarboxylicdianhydride, perylene 3,4,9,10-tetracarboxylic dianhydride,tetrahydrofuran tetracarboxylic dianhydride, 1,3-bis-(4,4′-oxydiphthalicanhydride) benzene, 2,2-bis(3,4-dicarboxyphenyl) propane dianhydride,2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,phenanthrene-1,8,9,10-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride,benzene-1,2,3,4-tetracarboxylic dianhydride andthiophene-2,3,4,5-tetracarboxylic dianhydride.

In one embodiment, a suitable additional dianhydride can include analicyclic dianhydride, such as cyclobutane-1,2,3,4-tetracarboxylicdiandydride (CBDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride,1,2,3,4-cyclohexanetetracarboxylic dianhydride,1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA),hexahydro-4,8-ethano-1H,3H-benzo[1,2-c:4,5-c′]difuran-1,3,5,7-tetrone(BODA), 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic1,4:2,3-dianhydride (TCA), and meso-butane-1,2,3,4-tetracarboxylicdianhydride. In one embodiment, an alicyclic dianhydride can be presentin an amount of about 70 mole percent or less, based on the totaldianhydride content of the polyimide.

In one embodiment, a suitable additional dianhydride for forming thepolyimide film can include a fluorinated dianhydride, such as4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 9,9-bis(trifluoromethyl)-2,3,6,7-xanthene tetracarboxylic dianhydride. In aspecific embodiment, the fluorinated dianhydride is4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA).

Crosslinking Agents

In one embodiment, crosslinking agents are used to make the polymerfilm. By crosslinking the polyimide, the polymer film may have improvedmechanical properties, as well as improved chemical resistance.Crosslinking agents can include polyetheramines, such as Jeffamine®D-230, Jeffamine® D-400, Jeffamine® D-2000, Jeffamine® D-2010,Jeffamine® D-4000, Jeffamine® ED-600, Jeffamine® ED-900, Jeffamine®D-2003, Jeffamine® EDR-148, Jeffamine® THF-100, Jeffamine® THF-170,Jeffamine® SD-2001, Jeffamine® D-205 and Jeffamine® RFD-270, secondaryamines, such as piperazine, N,N′-diisopropylethylenediamine,N,N′-diisopropyl-1,3-propanediamine andN,N′-dimethyl-1,3-propanediamine, and triamines, such as2,4,6-triaminopyrimidine (TAP), melamine, diethylenetriamine, Jeffamine®T-403, Jeffamine® T-3000, Jeffamine® T-5000. In addition, many diaminesthat may be used as a diamine monomer for polyimides, as describedabove, may also be useful as crosslinking agents. In one embodiment, thepolyamic acid solution contains up to 10 mole percent of a crosslinkingagent, based on a composition with 100 mole percent of diamine and 85 to99 mole percent of dianhydride. After imidization of the polyamic acidto form the polyimide film, some or all of the crosslinking agent maystill remain in the polyimide film. In one embodiment the polyimide filmcontains up to 10 mole percent of a crosslinking agent, based on acomposition with 100 mole percent of diamine and 85 to 99 mole percentof dianhydride.

Colorants

In one embodiment, the polyimide film contains 1 to 40 wt % of acolorant, such as a pigment or dye. In some embodiments, the polyimidefilm contains 1 to 40 wt % of a mixture of pigments and dyes. In someembodiments, the polyimide film contains between and including any twoof the following: 1, 5, 10, 15, 20, 25, 30, 35 and 40 wt % colorant.

Virtually any pigment (or combination of pigments) can be used in theperformance of the present invention. In some embodiments, usefulpigments include but are not limited to the following: Barium LemonYellow, Cadmium Yellow Lemon, Cadmium Yellow Lemon, Cadmium YellowLight, Cadmium Yellow Middle, Cadmium Yellow Orange, Scarlet Lake,Cadmium Red, Cadmium Vermilion, Alizarin Crimson, Permanent Magenta, VanDyke brown, Raw Umber Greenish, or Burnt Umber. In some embodiments,useful black pigments include: cobalt oxide, Fe—Mn—Bi black, Fe—Mn oxidespinel black, (Fe,Mn)₂O₃ black, copper chromite black spinel, lampblack,bone black, bone ash, bone char, hematite, black iron oxide, micaceousiron oxide, black complex inorganic color pigments (CICP),(Ni,Mn,Co)(Cr,Fe)₂O₄ black, Aniline black, Perylene black, Anthraquinoneblack, Chromium Green-Black Hematite, Chrome Iron Oxide, Pigment Green17, Pigment Black 26, Pigment Black 27, Pigment Black 28, Pigment Brown29, Pigment Brown 35, Pigment Black 30, Pigment Black 32, Pigment Black33 or mixtures thereof.

In some embodiments, the pigment is lithopone, zinc sulfide, bariumsulfate, cobalt oxide, yellow iron oxide, orange iron oxide, red ironoxide, brown iron oxide, hematite, black iron oxide, micaceous ironoxide, chromium (III) green, ultramarine blue, ultramarine violet,ultramarine pink, cyanide iron blue, cadmium pigments or lead chromatepigments.

In some embodiments, the pigment is complex inorganic color pigments(CICP) such as spinel pigments, rutile pigments, zircon pigments orbismuth vanadate yellow. In some embodiments, useful spinel pigmentsinclude but are not limited to: Zn(Fe,Cr)₂O₄ brown, CoAl₂O₄ blue,Co(AlCr)₂O₄ blue-green, Co₂TiO₄ green, CuCr₂O₄ black or(Ni,Mn,Co)(Cr,Fe)₂O₄ black. In some embodiments, useful rutile pigmentsinclude but are not limited to: Ti—Ni—Sb yellow, Ti—Mn—Sb brown,Ti—Cr—Sb buff, zircon pigments or bismuth vanadate yellow.

In another embodiment, the pigment is an organic pigment. In someembodiments, useful organic pigments include but are not limited to:Aniline black (Pigment Black 1), Anthraquinone black, Monoazo type,Diazo type, Benzimidazolones, Diarylide yellow, Monoazo yellow salts,Dinitaniline orange, Pyrazolone orange, Azo red, Naphthol red, Azocondensation pigments, Lake pigments, Copper Phthalocyanine blue, CopperPhthalocyanine green, Quinacridones, Diaryl Pyrrolopyrroles,Aminoanthraquinone pigments, Dioxazines, Isoindolinones, Isoindolines,Quinophthalones, phthalocyanine pigments, idanthrone pigments, pigmentviolet 1, pigment violet 3, pigment violet 19 or pigment violet 23. Inyet another embodiment, the organic pigment is a Vat dye pigment, suchas but not limited to: perylene, perylene black, perinones orthioindigo. A uniform dispersion of isolated, individual pigmentparticles (aggregates) tends to produce uniform color intensity. In someembodiments, the pigment is milled. In some embodiments, the meanparticle size of the pigment is between (and optionally including) anytwo of the following sizes: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and1.0 μm. In some embodiments, luminescent (fluorescent orphosphorescent), or pearlescent pigments can be used, alone, or incombination with other pigments or dyes.

In one embodiment, the colorant may include low conductivity carbonblack. In some embodiments, the colorant contains between and includingany two of the following: 1, 5, 10, 15 and 20 wt % low conductivitycarbon black. In yet another embodiment, the colorant includes 2 to 9 wt% low conductivity carbon black.

Low conductivity carbon black is intended to mean, channel type black,furnace black or lamp black. In some embodiments, the low conductivitycarbon black is a surface oxidized carbon black. One method forassessing the extent of surface oxidation (of the carbon black) is tomeasure the carbon black's volatile content. The volatile content can bemeasured by calculating weight loss when calcined at 950° C. for 7minutes. Generally speaking, a highly surface oxidized carbon black(high volatile content) can be readily dispersed into a polymerprecursor solution, which in turn can be imidized into a (welldispersed) filled polymer of the present disclosure. It is thought thatif the carbon black particles (aggregates) are not in contact with eachother, then electron tunneling, electron hopping or other electron flowmechanism are generally suppressed, resulting in lower electricalconductivity. In some embodiments, the low conductivity carbon black hasa volatile content greater than or equal to 1%. In some embodiments, thelow conductivity carbon black has a volatile content greater than orequal to 5, 9, or 13%. In some embodiments, furnace black may be surfacetreated to increase the volatile content. Typically, a low conductivitycarbon black has a pH less than 6.

A uniform dispersion of isolated, carbon black particles (aggregates)not only decreases the electrical conductivity, but additionally tendsto produce uniform color intensity. In some embodiments, the lowconductivity carbon black is milled. In some embodiments, the meanparticle size of the low conductivity carbon black is between (andoptionally including) any two of the following sizes: 0.2, 0.3, 0.4,0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 μm.

Matting Agents

In one embodiment, the polyimide film contains 0.5 to 20 wt % of amatting agent selected from the group consisting of silica, alumina,zirconia, boron nitride, barium sulfate, polyimide particles, calciumphosphate, talc or mixtures thereof. In some embodiments, the polyimidefilm contains between and including any two of the following: 0.5, 1, 5,10, 15 and 20 wt % matting agent. In one embodiment, a matting agent hasa particle size in a range of from 2 to 10 μm, or from 3 to 9 μm, orfrom 5 to 7 μm.

Submicron Particles

In one embodiment, the polyimide film contains up to 39 wt % of at leastone submicron particle, such as a submicron fumed metal oxide (alsoknown as pyrogenic metal oxide) or a submicron colloidal metal oxide ora mixture thereof. In some embodiments, the submicron fumed metal oxideis fumed alumina, fumed silica or mixtures thereof. In one embodiment,the polyimide film includes up to 20 wt %, or up to 10 wt % of at leastone submicron particle. In one embodiment, a submicron particle has aparticle size of less than about 1 μm. In one embodiment, a submicronparticle has a particle size in a range of from 0.01 to 1 μm, or from0.05 to 0.5 μm.

The particle sizes of the submicron particles, carbon blacks and mattingagents can be measured in the slurries by laser diffraction using aparticle size analyzer, such as a LA-930 (Horiba, Instruments, Inc.,Irvine Calif.), Mastersizer 3000 (Malvern Instruments, Inc.,Westborough, Mass.) or LS-230 (Beckman Coulter, Inc., Indianapolis,Ind.). However, due to the tendency of the submicron particles toflocculate, it is sometimes more accurate to measure particle size ofthese milled slurries by observing in an optical microscope.

Polyimide Films

In one embodiment, a polyimide film can be produced by combining adiamine and a dianhydride (monomer or other polyimide precursor form)together with a solvent to form a polyamic acid solution. Thedianhydride and diamine can be combined in a molar ratio of from 0.85:1to 0.99:1, or from 0.90:1 to 0.99:1, or from 0.95:1 to 0.985:1, or from0.965:1 to 0.985:1. The molecular weight of the polyamic acid formedtherefrom can be adjusted by adjusting the molar ratio of thedianhydride and diamine, the solution viscosity, and the solids content.Instead of targeting dianhydride to diamine ratios of 1:1 or greaterthan 1:1, having a small deficit in the amount of dianhydride in thepolyimide (less than a 1:1 ratio) can lead to polyimide chainscontaining amine chain end and increase the film stability under higherhumidity and more acid environments. At these molar ratios, polyamicacid solutions with high viscosity and high solids content can bereadily processed to form robust, flexible films with high T_(g), lowCTE and high tensile modulus. In one embodiment, polyamic acid solutionshaving PMDA and DAPBI monomers can be prepared with viscosities in arange of from 300 to 3000 poise, while having solids contents in a rangeof from 10 to 25%, enabling large scale roll-to-roll processing to formpolyimide films. In one embodiment, the polyamic acid solution can havea viscosity in a range of from 500 to 2600, or from 1000 to 2400, orfrom 1300 to 2200 poise. In one embodiment, the polyamic acid solutioncan have a solids content in a range of from 13 to 25%, or from 16 to22%.

Useful methods for producing polyamic acid solutions in accordance withthe present invention can be found in U.S. Pat. No. 5,298,331, which isincorporate by reference into this specification for all teachingstherein. Numerous variations are also possible, such as,

(a) A method wherein diamines are exclusively dissolved in a solvent andthen dianhydrides are added thereto at such a ratio as allowing tocontrol the reaction rate.

(b) A method wherein the dianhydride components are exclusivelydissolved in a solvent and then diamine components are added thereto atsuch a ratio to allow control of the reaction rate.

(c) A method wherein the polyamic acid with excessive diamine componentand another polyamic acid with excessive dianhydride component arepreliminarily formed and then reacted with each other in a reactor,particularly in such a way as to create a non-random or block copolymer.

(d) A method wherein a specific portion of the diamine components andthe dianhydride components are first reacted and then the residualdiamine components are reacted, or vice versa.

(e) A method wherein the components are added in part or in whole in anyorder to either part or whole of the solvent, also where part or all ofany component can be added as a solution in part or all of the solvent.

(f) A method of first reacting one of the dianhydride components withone of the diamine components giving a first polyamic acid. Thenreacting another dianhydride component with another diamine component togive a second polyamic acid. Then combining the amic acids in any one ofa number of ways prior to imidization.

In one embodiment, a polyamic acid solution can be combined withconversion chemicals like: (i) one or more dehydrating agents, such as,aliphatic acid anhydrides and/or aromatic acid anhydrides (aceticanhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride,trifluoroacetic anhydride and others); and (ii) one or more catalysts,such as, aliphatic tertiary amines (triethyl amine, etc.), aromatictertiary amines (dimethyl aniline, etc.) and heterocyclic tertiaryamines (pyridine, alpha, beta and gamma picoline (2-methylpyridine,3-methylpyridine, 4-methylpyridine), isoquinoline, etc.).

In one embodiment, a conversion chemical can be an imidization catalyst(sometimes called an “imidization accelerator”) that can help lower theimidization temperature and shorten the imidization time. Typicalimidization catalysts can range from bases such as imidazole,1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole,2-phenylimidazole, benzimidazole, isoquinoline, substituted pyridinessuch as methyl pyridines, lutidine, and trialkylamines and hydroxy acidssuch as isomers of hydroxybenzoic acid. The ratio of these catalysts andtheir concentration in the polyamic acid layer will influenceimidization kinetics and the film properties.

In one embodiment, the polyamic acid solution can be heated, optionallyin the presence of the imidization catalyst, to partially or fullyimidize the polyamic acid, converting it to a polyimide. Temperature,time, and the concentration and choice of imidization catalyst canimpact the degree of imidization of the polyamic acid solution.Preferably, the solution should be substantially imidized. In oneembodiment, for a substantially polyimide solution, greater than 85%,greater than 90%, or greater than 95% of the amic acid groups areconverted to the polyimide, as determined by infrared spectroscopy.

In one embodiment, the solvated mixture (the substantially imidizedsolution) can be cast to form a polyimide film. In another embodiment,the solvated mixture (the first substantially imidized solution) can beprecipitated with an antisolvent, such as water or alcohols (e.g.,methanol, ethanol, isopropyl alcohol), and the solid polyimide resin canbe isolated. For instance, isolation can be achieved through filtration,decantation, centrifugation and decantation of the supernatant liquid,distillation or solvent removal in the vapor phase, or by other knownmethods for isolating a solid precipitate from a slurry. In oneembodiment, the precipitate can be washed to remove the catalyst. Afterwashing, the precipitate may be substantially dried, but need not becompletely dry. The polyimide precipitate can be re-dissolved in asecond solvent, such as methyl isobutyl ketone (MIBK), methyl ethylketone (MEK), ethyl acetate, methyl acetate, ethyl formate, methylformate, tetrahydrofuran, acetone, DMAc, NMP and mixtures thereof, toform a second substantially imidized solution (a casting solution),which can be cast to form a polyimide film.

The casting solution can further comprise any one of a number ofadditives, such as processing aids (e.g., oligomers), antioxidants,light stabilizers, flame retardant additives, anti-static agents, heatstabilizers, ultraviolet absorbing agents, inorganic fillers or variousreinforcing agents. Inorganic fillers can include thermally conductivefillers, metal oxides, inorganic nitrides and metal carbides. Commoninorganic fillers are alumina, silica, diamond, clay, boron nitride,aluminum nitride, titanium dioxide, dicalcium phosphate, and fumed metaloxides. Low color organic fillers, such as polydialkylfluorenes, canalso be used.

In one embodiment, the elastic modulus of a polyimide film can beincreased by the presence of sub-micron fillers. The sub-micron fillercan be inorganic or organic and can be present in an amount between andoptionally including any two of the following percentages: 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55 and 60 weight percent of the polyimidefilm.

In one embodiment the sub-micron filler can have a size of less than 550nm in at least one dimension. In other embodiments, the filler can havea size of less than 500, less than 450, less than 400, less than 350,less than 300, less than 250, less than 200 nm, or less than 100 nm inat least one dimension (since fillers can have a variety of shapes inany dimension and since filler shape can vary along any dimension, the“at least one dimension” is intended to be a numerical average alongthat dimension). The average aspect ratio of the filler can be 1, forspherical particles, or greater than 1 for non-spherical particles. Insome embodiments, the sub-micron filler is selected from a groupconsisting of needle-like fillers (acicular), fibrous fillers, plateletfillers, polymer fibers, and mixtures thereof. In one embodiment, thesub-micron filler is substantially non-aggregated. The sub-micron fillercan be hollow, porous, or solid, or can have a core-shell structurewhere one composition is in the core and a second composition is in theshell. In one embodiment, the sub-micron fillers of the presentdisclosure exhibit an aspect ratio of at least 1:1, at least 2:1, atleast 4:1, at least 6:1, at least 8:1, at least 10:1, at least 12:1, orat least 15:1.

In some embodiments, sub-micron fillers are 100 nm in size or less in atleast one dimension. In some embodiments, the fillers are spherical,lenticular or oblong in shape and are nanoparticles. In one embodiment,sub-micron fillers can include inorganic oxides, such as oxides ofsilicon, aluminum and titanium, hollow (porous) silicon oxide, antimonyoxide, zirconium oxide, indium tin oxide, antimony tin oxide, mixedtitanium/tin/zirconium oxides, and binary, ternary, quaternary andhigher order composite oxides of one or more cations selected fromsilicon, titanium, aluminum, antimony, zirconium, indium, tin, zinc,niobium and tantalum. In one embodiment, nanoparticle composites (e.g.single or multiple core/shell structures) can be used, in which oneoxide encapsulates another oxide in one particle.

In one embodiment, sub-micron fillers can include other ceramiccompounds, such as boron nitride, aluminum nitride, ternary or higherorder compounds containing boron, aluminum and nitrogen, galliumnitride, silicon nitride, aluminum nitride, zinc selenide, zinc sulfide,zinc telluride, and their combinations, or higher order compoundscontaining multiple cations and multiple anions.

In one embodiment, solid silicon oxide nanoparticles can be producedfrom sols of silicon oxides (e.g., colloidal dispersions of solidsilicon oxide nanoparticles in liquid media), especially sols ofamorphous, semi-crystalline, and/or crystalline silica. Such sols can beprepared by a variety of techniques and in a variety of forms, whichinclude hydrosols (i.e., where water serves as the liquid medium),organosols (i.e., where organic liquids serves as the liquid medium),and mixed sols (i.e., where the liquid medium comprises both water andan organic liquid). See, e.g., descriptions of the techniques and formsdisclosed in U.S. Pat. Nos. 2,801,185, 4,522,958 and 5,648,407. In oneembodiment, the nanoparticle is suspended in a polar, aprotic solvent,such as, DMAc or other solvent compatible with polyamic acid orpolyimide solution. In another embodiment, solid silicon oxidenanoparticles can be commercially obtained as colloidal dispersions orsols dispersed in polar aprotic solvents, such as for example DMAC-ST(Nissan Chemical America Corporation, Houston, Tex.), a solid silicacolloid in dimethylacetamide containing less than 1 percent water byweight, with 20-21 wt % SiO₂, with a median nanosilica particle diameterd₅₀ of about 20 nm.

In one embodiment, sub-micron fillers can be porous and can have poresof any shape. One example is where the pore comprises a void of lowerdensity and low refractive index (e.g., a void containing air) formedwithin a shell of an oxide such as silicon oxide, i.e., a hollow siliconoxide nanoparticle. The thickness of the sub-micron fillers shellaffects the strength of the sub-micron fillers. As the hollow siliconoxide particle is rendered to have reduced refractive index andincreased porosity, the thickness of the shell decreases resulting in adecrease in the strength (i.e., fracture resistance) of the sub-micronfillers. Methods for producing such hollow silicon oxide nanoparticlesare known, for example, as described in Japanese Patent Nos. 4406921B2and 4031624B2. Hollow silicon oxide nanoparticles can be obtained fromJGC Catalysts and Chemicals, LTD, Japan.

In one embodiment, sub-micron fillers can be coated with a couplingagent. For example, a nanoparticle can be coated with an aminosilane,phenylsilane, acrylic or methacrylic coupling agents derived from thecorresponding alkoxysilanes. Trimethylsilyl surface capping agents canbe introduced to the nanoparticle surface by reaction of the sub-micronfillers with hexamethyldisilazane. In one embodiment, sub-micron fillerscan be coated with a dispersant. In one embodiment, sub-micron fillerscan be coated with a combination of a coupling agent and a dispersant.Alternatively, the coupling agent, dispersant or a combination thereofcan be incorporated directly into the polyimide film and not necessarilycoated onto the sub-micron fillers.

In some embodiments, the sub-micron filler is chosen so that it does notitself degrade or produce off-gasses at the desired processingtemperatures. Likewise, in some embodiments, the sub-micron filler ischosen so that it does not contribute to degradation of the polymer.

In one embodiment, a polyamic acid solution can form a “green film”which is partially polyamic acid and partially polyimide, and may beformed in a thermal conversion process. Green film generally containsabout 50 to 75 wt % polymer and 25 to 50 wt % solvent. Generally, itshould be sufficiently strong to be substantially self-supporting. Greenfilm can be prepared by casting the polyamic acid solution into filmform onto a suitable support such as a casting drum or belt and removingthe solvent by mild heating at up to 150° C. A low proportion of amicacid units in the polymer, e.g., up to 25%, may be converted to imideunits. In one embodiment, the polyamic acid solution can be cast orapplied onto a support, such as an endless belt or rotating drum, toform a green film. Alternatively, it can be cast on a polymeric carriersuch as PET, other forms of Kapton® polyimide film (e.g., Kapton® HN orKapton® OL films) or other polymeric carriers. Next, the solventcontaining-film can be converted into a polyimide film by heating topartially or fully remove the solvent. In some aspects of the invention,the green film is separated from the carrier before drying tocompletion. Final drying steps can be performed with dimensional supportor stabilization of the film. In other aspects, the wet film is heateddirectly on the carrier.

In one embodiment, a substantially imidized polyimide solution can becast or applied onto a support, such as an endless belt or rotatingdrum, to form a film. Alternatively, it can be cast on a polymericcarrier such as PET, other forms of Kapton® polyimide film (e.g.,Kapton® HN or Kapton® OL films) or other polymeric carriers. Next, thesolvent containing-film can be converted into a film by heating topartially or fully remove the solvent. In some aspects of the invention,the film is separated from the carrier before drying to completion.Final drying steps can be performed with dimensional support orstabilization of the film. In other aspects, the film is heated directlyon the carrier.

The thickness of the polyimide film may be adjusted, depending on theintended purpose of the film or final application specifications. In oneembodiment, the polyimide film has a total thickness in a range of from4 to 150 μm, or from 5 to 100 μm, or from 10 to 80 μm.

When polyimide film is used as a flexible TFT substrate for anelectronic device, such as a flexible OLED display, E-Paper or sensor,the tensile modulus of the substrate film must have a high modulus (>6.0GPa) because the polyimide film, supported by a glass substrate will gothrough the TFT formation process and subsequently need to peel off ofthe glass substrate (debonding) smoothly without film deformation.Typically, film-glass laminates will undergo high temperature TFT (thinfilm transistor) processing for extended periods of time at 450° C., sothe T_(g) of the polyimide film must at least be above 400° C. tomaintain good mechanical properties of the film throughout the TFTmanufacturing process. The CTE match between the polyimide film andglass substrate must also be good to limit thermal stresses at thepolymer/glass interface and avoid delamination, curling andfilm-cracking during TFT processing. In one embodiment, the polyimidefilm has a tensile modulus of 6.0 GPa or more, or 7.0 GPa or more, or8.0 GPa or more. In one embodiment, the polyimide film has a T_(g) of400° C. or higher, or 425° C. or higher, or 450° C. or higher. In oneembodiment, the polyimide film has a coefficient of thermal expansion of15 ppm/° C. or less, or 10 ppm/° C. or less, or 5 ppm/° C. or less, overa temperature range of 50 to 500° C.

Metal-Clad Laminates

In one embodiment, a conductive layer of the present invention can becreated by:

-   -   i. metal sputtering (optionally, then electroplating);    -   ii. foil lamination; and/or    -   iii. any conventional or non-conventional method for applying a        thin metallic layer to a substrate.

Metal-clad laminates can be formed as single-sided laminates ordouble-sided laminates by any number of well-known processes. In oneembodiment, a lamination process may be used to form a metal-cladlaminate with a polymer film or multilayer polyimide film. In oneembodiment, a first outer layer including a first thermoplasticpolyimide is placed between a first conductive layer and a core layer,and a second outer layer including a second thermoplastic polyimide isplaced on the opposite side of the core layer. In one embodiment, asecond conductive layer is placed in contact with the second outer layeron a side opposite the core layer. One advantage of this type ofconstruction is that the lamination temperature of the multilayer filmis lowered to the lamination temperature necessary for the thermoplasticpolyimide of the outer layer to bond to a conductive layer(s). In oneembodiment, the conductive layer(s) is a metal layer(s).

For example, prior to the step of applying a polymer film onto a metalfoil, the polymer film can be subjected to a pre-treatment step.Pre-treatment steps can include, heat treatment, corona treatment,plasma treatment under atmospheric pressure, plasma treatment underreduced pressure, treatment with coupling agents like silanes andtitanates, sandblasting, alkali-treatment, acid-treatments, and coatingpolyamic acids. To improve the adhesion strength, it is generally alsopossible to add various metal compounds as disclosed in U.S. Pat. Nos.4,742,099; 5,227,244; 5,218,034; and 5,543,222, incorporated herein byreference.

In addition, (for purposes of improving adhesion) the conductive metalsurface may be treated with various organic and inorganic treatments.These treatments include using silanes, imidazoles, triazoles, oxide andreduced oxide treatments, tin oxide treatment, and surfacecleaning/roughening (called micro-etching) via acid or alkalinereagents.

In a further embodiment, the polyamic acid precursor (to a polyimidefilm of the present invention) may be coated on a fully cured polyimidebase film or directly on a metal substrate and subsequently imidized byheat treatment. The polyimide base film may be prepared by either achemical or thermal conversion process and may be surface treated, e.g.by chemical etching, corona treatment, laser etching etc., to improveadhesion.

As used herein, the term “conductive layers” and “conductive foils” meanmetal layers or metal foils (thin compositions having at least 50% ofthe electrical conductivity of a high-grade copper). Conductive foilsare typically metal foils. Metal foils do not have to be used aselements in pure form; they may also be used as metal foil alloys, suchas copper alloys containing nickel, chromium, iron, and other metals.The conductive layers may also be alloys of metals and are typicallyapplied to the polyimides of the present invention via a sputtering stepfollowed by an electro-plating step. In these types of processes, ametal seed coat layer is first sputtered onto a polyimide film. Finally,a thicker coating of metal is applied to the seed coat viaelectro-plating or electro-deposition. Such sputtered metal layers mayalso be hot pressed above the glass transition temperature of thepolymer for enhanced peel strength.

Particularly suitable metallic substrates are foils of rolled, annealedcopper or rolled, annealed copper alloy. In many cases, it has proved tobe advantageous to pre-treat the metallic substrate before coating. Thispre-treatment may include, but is not limited to, electro-deposition orimmersion-deposition on the metal of a thin layer of copper, zinc,chrome, tin, nickel, cobalt, other metals, and alloys of these metals.The pre-treatment may consist of a chemical treatment or a mechanicalroughening treatment. It has been found that this pre-treatment enablesthe adhesion of the polyimide layer and, hence, the peel strength to befurther increased. Apart from roughening the surface, the chemicalpre-treatment may also lead to the formation of metal oxide groups,enabling the adhesion of the metal to a polyimide layer to be furtherincreased. This pre-treatment may be applied to both sides of the metal,enabling enhanced adhesion to substrates on both sides.

In one embodiment, a metal-clad laminate can include the polymer filmthat is a single-layer film or a multilayer film and a first metal layeradhered to an outer surface of the first outer layer of the multilayerfilm. In one embodiment, a metal-clad laminate can include a secondmetal layer adhered to an outer surface of the second outer layer of themultilayer film. In one embodiment, the first metal layer, the secondmetal layer or both metal layers can be copper. In one embodiment, ametal-clad laminate of the present invention comprising a double-sidecopper-clad can be prepared by laminating copper foil to both sides ofthe single-layer or multilayer film.

Applications

In one embodiment, a polyimide film with high T_(g), high tensilestrength and low CTE can be used in electronic device applications, suchas flexible device layers for electronic device or a coverlay for aprinted circuit board or other electronic components in an electronicdevice, providing protection from physical damage, oxidation and othercontaminants that may adversely affect the function of the electroniccomponents.

In one embodiment, a polyimide film that is a flexible device layer canbe used for any number of layers in electronic device applications, suchas in an organic electronic device, where a combination of good hightemperature resistance stability and excellent mechanical properties isdesirable. Nonlimiting examples of such layers include thin-filmtransistor (TFT) substrates for flexible displays, such as organiclight-emitting diode (OLED) displays, electronic paper (E-paper) andtouch sensor panels (TSPs), substrates for color filter sheets, coverfilms, and other device layers. The particular materials' propertiesrequirements for each application are unique and may be addressed byappropriate composition(s) and processing condition(s) for the polyimidefilms disclosed herein. Organic electronic devices that may benefit fromhaving a polyimide film include, but are not limited to, (1) devicesthat convert electrical energy into radiation (e.g., a light-emittingdiode, light emitting diode display, lighting device, luminaire, ordiode laser), (2) devices that detect signals through electronicsprocesses (e.g., photodetectors, photoconductive cells, photoresistors,photoswitches, phototransistors, phototubes, IR detectors, biosensors),(3) devices that convert radiation into electrical energy, (e.g., aphotovoltaic device or solar cell), (4) devices that convert light ofone wavelength to light of a longer wavelength, (e.g., a down-convertingphosphor device); and (5) devices that include one or more electroniccomponents that include one or more organic semi-conductor layers (e.g.,a transistor or diode).

In one embodiment, a metal-clad laminate having a polyimide film isparticularly useful for die pad bonding of flexible print connectionboards or semiconductor devices or packaging materials for CSP (chipscale package), chip on film (COF), COL (chip on lead), LOC (lead onchip), multi-chip module (“MCM”), ball grid array (“BGA” or micro-ballgrid array), and/or tape automated bonding (“TAB”).

In another embodiment, the polyimide films are useful for wafer levelintegrated circuit packaging, where a composite is made using apolyimide film interposed between a conductive layer (typically a metal)having a thickness of less than 100 μm, and a wafer comprising aplurality of integrated circuit dies. In one (wafer level integratedcircuit packaging) embodiment, the conductive passageway is connected tothe dies by a conductive passageway, such as a wire bond, a conductivemetal, a solder bump or the like.

The advantageous properties of this invention can be observed byreference to the following examples that illustrate, but do not limit,the invention. All parts and percentages are by weight unless otherwiseindicated.

EXAMPLES Test Methods

Glass Transition Temperature and Storage Modulus

Glass transition temperature (T_(g)) and storage modulus at 50° C. and400° C. were measured using dynamic mechanical analysis (Q800 DMA, TAInstruments, New Castle, Del.). These DMA profiles of the films werecollected over the temperature range of 25° C. to 520° C. at a heatingrate of 5° C./min.

Coefficient of Thermal Expansion

Coefficient of thermal expansion (CTE) in both the machine direction(MD) and transverse direction (TD) of the films were measure bythermomechanical analysis (Q400 TMA, TA Instruments).

Tensile Modulus, Tensile Strength, and Elongation to Break

Tensile properties (modulus, strength and elongation to break) of filmswere measured at room temperature following the ASTM D882 test methodusing 0.5×4″ film samples and a cross-head speed of 2 in/min.

Thickness

Coating thickness was determined by measuring coated and uncoatedsamples in 10 positions across the TD direction of the film using acontact-type FISCHERSCOPE MMS PC2 modular measurement system thicknessgauge (Fisher Technology Inc., Windsor, Conn.).

Peel Strength

Peel strengths were measured using 0.5×3″ film samples. The crossheadpeeling speed was 2 in/min using a 90° German wheel configurationfollowing IPC test method 2.4.9D for die-cut specimens. CTE, dielectricconstant (D_(k)) and dissipation factor (D_(f)) values of the polyimidefilms in copper-clads are collected after etching off the entire Cu foilof each sample.

Comparative Example 1

For Comparative Example 1 (CE1), to prepare a polyamic acid (PAA) with amonomer composition of PMDA 1.0//PPD 0.7/ODA 0.3, 6.497 g ofp-phenylenediamine (PPD) and 5.156 g of 4,4′-diaminodiphenyl ether (ODA)were mixed into 120 g of dimethylacetamide (DMAc) at 25° C., stirring at150 rpm. 18.347 g of pyromellitic dianhydride (PMDA) was then added andthe mixture was allowed to stir for 3 hours. The prepolymer solution wasadjusted (“finished”) to ˜2000 poise using small additions of 6 wt %PMDA solution in DMAc while stirring at 50 rpm.

To prepare a film, the PAA solution was mixed for 2 minutes in acentrifugal-planetary mixer (THINKY USA, Laguna Hills, Calif.) to obtaina solution. The solution was de-gassed using the centrifugal-planetarymixer to force the gas from the polymer at 2000 rpm for 20 minutes andthen cast onto a glass plate at 25° C. using a metal bar to produce ˜1.5mil dried films. The film on the glass substrate was heated to 120° C.for 80 minutes on a hot plate, resulting in a green film with 65-70%solids, and subsequently lifted off the glass surface and mounted onto a10×10 inch pin frame. The mounted film was placed in a furnace andheated from 120 to 340° C. (10° C./min), transferred to a 400° C.furnace and held for 8 minutes. The films were removed “hot” from theoven and allowed to cool in air.

Comparative Example 2

For Comparative Example 2 (CE2), to prepare a PAA with a monomercomposition of PMDA 1.0//MPD 0.35/PPD 0.35/ODA 0.3, 3.249 g of PPD,3.249 g of m-phenylenediamine (MPD) and 5.156 g of ODA were mixed into120 g of DMAc, followed by the addition of 18.347 g of PMDA, and thenfinishing to ˜2000 poise, all following the procedure of CE1. Films werealso prepared following the procedure of CE1.

Comparative Example 3

For Comparative Example 3 (CE3), to prepare a PAA with a monomercomposition of PMDA 1.0//MPD 0.7/ODA 0.3, 6.497 g of MPD and 5.156 g ofODA were mixed into 120 g of DMAc, followed by the addition of 18.347 gof PMDA, and then finishing to ˜2000 poise, all following the procedureof CE1. Films were also prepared following the procedure of CE1.

Comparative Example 4

For Comparative Example 4 (CE4), to prepare a PAA with a monomercomposition of PMDA 1.0//DAPBI 0.35/PPD 0.35/ODA 0.3, 6.035 g of5-amino-2-(4-aminophenyl)benzimidazole (DAPBI), 2.910 g of PPD and 4.619g of ODA were mixed into 120 g of DMAc, followed by the addition of16.436 g of PMDA, and then finishing to ˜2000 poise, all following theprocedure of CE1. Films were also prepared following the procedure ofCE1.

Comparative Example 5

For Comparative Example 5 (CE5), to prepare a PAA with a monomercomposition of PMDA 1.0//DAPBI 0.35/MPD 0.35/ODA 0.3, 6.035 g of DAPBI,2.910 g of MPD and 4.619 g of ODA were mixed into 120 g of DMAc,followed by the addition of 16.436 g of PMDA, and then finishing to˜2000 poise, all following the procedure of CE1. Films were alsoprepared following the procedure of CE1.

Comparative Example 6

For Comparative Example 6 (CE6), to prepare a PAA with a monomercomposition of PMDA 0.7/BPDA 0.3//PPD 0.7/ODA 0.3, 6.099 g of PPD and4.840 g of ODA were mixed into 120 g of DMAc, followed by the additionof 11.950 g of PMDA and 7.111 g of 3,3′,4,4′-biphenyltetracarboxylicdianhydride (s-BPDA), and then finishing to ˜2000 poise, all followingthe procedure of CE1. Films were also prepared following the procedureof CE1.

Comparative Example 7

For Comparative Example 7 (CE7), to prepare a PAA with a monomercomposition of PMDA 0.3/BPDA 0.7//PPD 0.7/ODA 0.3, 5.638 g of PPD and4.474 g of ODA were mixed into 120 g of DMAc, followed by the additionof 4.549 g of PMDA and 15.339 g of s-BPDA, and then finishing to ˜2000poise, all following the procedure of CE1. Films were also preparedfollowing the procedure of CE1.

Comparative Example 8

For Comparative Example 8 (CE8), to prepare a PAA with a monomercomposition of PMDA 0.7/BPDA 0.3//PPD 0.7/DAPBI 0.3, 5.983 g of PPD and5.318 g of DAPBI were mixed into 120 g of DMAc, followed by the additionof 11.723 g of PMDA and 6.976 g of s-BPDA, and then finishing to ˜2000poise, all following the procedure of CE1. Films were also preparedfollowing the procedure of CE1.

Comparative Example 9

For Comparative Example 9 (CE9), to prepare a PAA with a monomercomposition of PMDA 0.3/BPDA 0.7//PPD 0.7/DAPBI 0.3, 5.539 g of PPD and4.923 g of DAPBI were mixed into 120 g of DMAc, followed by the additionof 4.469 g of PMDA and 15.070 g of s-BPDA, and then finishing to ˜2000poise, all following the procedure of CE1. Films were also preparedfollowing the procedure of CE1.

Comparative Example 10

For Comparative Example 10 (CE10), to prepare a PAA with a monomercomposition of BPDA 1.0//DAPBI 1.0, 13.086 g of DAPBI was mixed into 120g of DMAc, followed by the addition of 17.168 g of s-BPDA, and thenfinishing to ˜2000 poise, all following the procedure of CE1. Films werealso prepared following the procedure of CE1.

Comparative Example 11

For Comparative Example 11 (CE11), to prepare a PAA with a monomercomposition of PMDA 1.0//PPD 0.3/ODA 0.7, 2.519 g of PPD and 10.884 g ofODA were mixed into 120 g of DMAc, followed by the addition of 16.597 gof PMDA, and then finishing to ˜2000 poise, all following the procedureof CE1. Films were also prepared following the procedure of CE1.

Example 1

For Example 1 (E1), to prepare a PAA with a monomer composition of PMDA1.0//DAPBI 1.0, 12.411 g of DAPBI was mixed into 126 g of DMAc at 25°C., stirring at 150 rpm forming an opaque solution. 11.589 g of PMDA wasthen added and the mixture became transparent and was allowed to stirfor 3 hours. The prepolymer solution was adjusted (“finished”) to 2048poise using small additions of 6 wt % PMDA solution in DMAc whilestirring at 50 rpm, reaching a final stoichiometry of 0.97:1 dianhydrideto diamine. Films were prepared following the procedure of CE1.

Example 2

For Example 2 (E2), to prepare a PAA with a monomer composition of PMDA0.9/BPDA 0.1//DAPBI 1.0, 12.197 g of DAPBI was mixed into 126 g of DMAc,followed by the addition of 10.202 g of PMDA and 1.600 g of s-BPDA, andthen finishing to 2377 poise, all following the procedure of E1. Thefinal stoichiometry was 0.981:1 dianhydride to diamine. Films wereprepared following the procedure of CE1.

Example 3

For Example 3 (E3), to prepare a PAA with a monomer composition of PMDA0.85/BPDA 0.15//DAPBI 1.0, 15.987 g of DAPBI was mixed into 168 g ofDMAc, followed by the addition of 11.818 g of PMDA and 4.195 g ofs-BPDA, and then finishing to 2208 poise, all following the procedure ofE1. Films were prepared following the procedure of CE1.

Example 4

For Example 4 (E4), to prepare a PAA with a monomer composition of PMDA0.8/BPDA 0.2//DAPBI 1.0, 12.093 g of DAPBI was mixed into 126 g of DMAc,followed by the addition of 9.527 g of PMDA and 2.380 g of s-BPDA, andthen finishing to 2250 poise, all following the procedure of E1. Filmswere prepared following the procedure of CE1, except that they were heldat 400° C. for 7 minutes instead of 8 minutes.

Example 5

For Example 5 (E5), to prepare a PAA with a monomer composition of PMDA0.7/BPDA 0.3//DAPBI 1.0, 15.721 g of DAPBI was mixed into 168 g of DMAc,followed by the addition of 10.092 g of PMDA and 6.188 g of s-BPDA, andthen finishing to 2180 poise, all following the procedure of E1. Filmswere prepared following the procedure of CE1.

Example 6

For Example 6 (E6), to prepare a PAA with a monomer composition of PMDA1.0//DAPBI 0.9/PPD 0.1, 11.478 g of DAPBI and 0.615 g of PPD were mixedinto 126 g of DMAc, followed by the addition of 11.907 g of PMDA, andthen finishing to 1934 poise, all following the procedure of E1. Filmswere prepared following the procedure of CE1.

Example 7

For Example 7 (E7), to prepare a PAA with a monomer composition of PMDA0.9/BPDA 0.1//DAPBI 0.9/PPD 0.1, 11.274 g of DAPBI and 0.604 g of PPDwere mixed into 126 g of DMAc, followed by the addition of 10.478 g ofPMDA and 1.643 g of s-BPDA, and then finishing to 1820 poise, allfollowing the procedure of E1. Films were prepared following theprocedure of CE1.

Example 8

For Example 8 (E8), to prepare a PAA with a monomer composition of PMDA1.0//DAPBI 0.8/PPD 0.2, 10.491 g of DAPBI and 1.265 g of PPD were mixedinto 126 g of DMAc, followed by the addition of 12.244 g of PMDA, andthen finishing to 2231 poise, all following the procedure of E1. Filmswere prepared following the procedure of CE1.

Example 9

For Example 9 (E9), to prepare a PAA with a monomer composition of PMDA0.9/BPDA 0.1//DAPBI 0.8/PPD 0.2, 10.300 g of DAPBI and 1.242 g of PPDwere mixed into 126 g of DMAc, followed by the addition of 10.769 g ofPMDA and 1.689 g of s-BPDA, and then finishing to 2341 poise, allfollowing the procedure of E1. Films were prepared following theprocedure of CE1.

Example 10

For Example 10 (E10), to prepare a PAA with a monomer composition ofPMDA 1.0//DAPBI 0.9/MPD 0.1, 11.478 g of DAPBI and 0.615 g of MPD weremixed into 126 g of DMAc, followed by the addition of 11.907 g of PMDA,and then finishing to 2011 poise, all following the procedure of E1.Films were prepared following the procedure of CE1.

Example 11

For Example 11 (E11), to prepare a PAA with a monomer composition ofPMDA 0.9/BPDA 0.1//DAPBI 0.9/MPD 0.1, 11.274 g of DAPBI and 0.604 g ofMPD were mixed into 126 g of DMAc, followed by the addition of 10.478 gof PMDA and 1.643 g of s-BPDA, and then finishing to 2194 poise, allfollowing the procedure of E1. Films were prepared following theprocedure of CE1.

Example 12

For Example 12 (E12), to prepare a PAA with a monomer composition ofPMDA 1.0//DAPBI 0.8/MPD 0.2, 10.491 g of DAPBI and 1.265 g of MPD weremixed into 126 g of DMAc, followed by the addition of 12.244 g of PMDA,and then finishing to 1280 poise, all following the procedure of E1.Films were prepared following the procedure of CE1.

Example 13

For Example 13 (E13), to prepare a PAA with a monomer composition ofPMDA 0.9/BPDA 0.1//DAPBI 0.8/MPD 0.2, 10.300 g of DAPBI and 1.242 g ofMPD were mixed into 126 g of DMAc, followed by the addition of 10.769 gof PMDA and 1.689 g of s-BPDA, and then finishing to 1331 poise, allfollowing the procedure of E1. Films were prepared following theprocedure of CE1.

Example 14

For Example 14 (E14), to prepare a PAA with a monomer composition ofPMDA 0.7/BPDA 0.3//DAPBI 0.7/PPD 0.3, 8.935 g of DAPBI and 1.847 g ofPPD were mixed into 126 g of DMAc, followed by the addition of 8.194 gof PMDA and 5.024 g of s-BPDA, and then finishing to ˜2000 poise, allfollowing the procedure of E1. Films were prepared following theprocedure of CE1.

Example 15

For Example 15 (E15), to prepare a PAA with a monomer composition ofPMDA 0.3/BPDA 0.7//DAPBI 0.7/PPD 0.3, 8.334 g of DAPBI and 1.722 g ofPPD were mixed into 126 g of DMAc, followed by the addition of 3.011 gof PMDA and 10.933 g of s-BPDA, and then finishing to ˜2000 poise, allfollowing the procedure of E1. Films were prepared following theprocedure of CE1.

Example 16

For Example 16 (E16), to prepare a PAA with a monomer composition ofPMDA 0.3/BPDA 0.7//DAPBI 0.5/PPD 0.5, 6.275 g of DAPBI and 3.026 g ofPPD were mixed into 126 g of DMAc, followed by the addition of 3.174 gof PMDA and 11.526 g of s-BPDA, and then finishing to 1200 poise, allfollowing the procedure of E1. Films were prepared following theprocedure of CE1.

Example 17

For Example 17 (E17), to prepare a PAA with a monomer composition ofPMDA 1.0//DAPBI 1.0, 12.411 g of DAPBI was mixed into 126 g of DMAc at30° C., stirring at 150 rpm forming an opaque solution. 11.589 g of PMDAwas then added and the mixture became transparent and was allowed tostir for 3 hours. The prepolymer solution was adjusted (“finished”) to3000 poise using small additions of 6 wt % PMDA solution in DMAc whilestirring at 50 rpm, reaching a final stoichiometry of 0.981:1dianhydride to diamine.

To prepare a soluble polyimide solution, the solids content was reducedfrom 16 wt % to 9.5 wt % by adding 103 g DMAc and stirring the PAAsolution for 1 hour. While keeping the solution at 40° C., 1.289 g ofbeta-picoline and 1.413 g of acetic anhydride were gradually added intothe PAA solution, making sure the viscosity of the solution was stable.The solution was stirred at 100 rpm and 80° C. for 7 hours and thencooled to room temperature.

To prepare a film, the polyimide solution was cast onto a glass plate at25° C. using a metal bar to produce˜1.5 mil dried films. The film on theglass substrate was heated to 80° C. for 20 minutes on a hot plate, andsubsequently lifted off the glass surface and mounted onto a 10×10 inchpin frame. The mounted film was placed in a furnace and heated from 120to 250° C. (10° C./min) and held at 250° C. for 20 minutes. The filmswere removed “hot” from the oven and allowed to cool in air.

Example 18

For Example 18 (E18), to prepare a PAA with a monomer composition ofPMDA 0.9/BPDA 0.1//DAPBI 1.0, 12.197 g of DAPBI was mixed into 126 g ofDMAc, followed by the addition of 10.202 g of PMDA and 1.600 g ofs-BPDA, and then finishing to 3000 poise, all following the procedure ofE17. The final stoichiometry was 0.985:1 dianhydride to diamine.

To prepare a soluble polyimide solution, the solids content was reducedfrom 16 wt % to 9.5 wt % by adding 103 g DMAc and stirring the PAAsolution for 1 hour. While keeping the solution at 40° C., 1.266 g ofbeta-picoline and 1.388 g of acetic anhydride were gradually added intothe PAA solution, making sure the viscosity of the solution was stable.The solution was stirred at 100 rpm and 80° C. for 7 hours and thencooled to room temperature. Films were prepared following the procedureof E17.

Table 1 summarizes the thermal and mechanical properties of CE1-CE11 andE1-E18. The CTE values of CE7, E15 and E16 were measured over 50-450° C.since their T_(g)'s are less than 450° C. The CTE values of E1 to E14are close to zero when measured over 50-450° C.

TABLE 1 DMA Diamine Modulus Modulus CTE Dianhydride T_(g) (MPa) (GPa)(50-500° C.) Modulus Example PMDA BPDA ODA DAPBI PPD MPD (tanΔ) 50° C.400° C. MD TD Avg (GPa) CE1 1 0.3 0.7 471 3972 2.3 39.7 43.8 41.7 4.0CE2 1 0.3 0.35 0.35 472.7 1782 1.3 63.3 55.7 59.5 2.8 CE3 1 0.3 0.7448.4 1188 1.2 65.0 63.1 64.0 2.5 CE4 1 0.3 0.35 0.35 457.7 3472 1.829.3 26.9 28.1 4.2 CE5 1 0.3 0.35 0.35 462.4 1937 1.3 29.6 27.3 28.5 3.5CE6 0.7 0.3 0.3 0.7 479.8 3015 1.7 64.9 57.6 61.3 3.3 CE7 0.3 0.7 0.30.7 331.9 4143 0.3 47.6* 33.2* 40.4* 3.9 CE8 0.7 0.3 0.3 0.7 449.5 47761.7 11.2 5.81 8.5 5.6 CE9 0.3 0.7 0.3 0.7 395.3 2121 0.2 — — — 5.2 CE101 1 414.3 2700 0.6 — — — 7.8 CE11 1 0.7 0.3 409.6 2538 0.5 54.1 53.753.9 3.2 E1 1 1 468.0 6582 4.0 −3.80 −4.35 −4.1 9.6 E2 0.9 0.1 1 463.97792 2.9 −1.31 −4.51 −2.9 8.6 E3 0.85 0.15 1 466.9 8076 3.3 −16.0 −9.01−12.5 10.3 E4 0.8 0.2 1 473.1 6949 2.8 −11.5 −7.76 −9.6 8.1 E5 0.7 0.3 1460.7 7525 3.0 6.22 8.11 7.17 7.6 E6 1 0.9 0.1 469.5 5014 2.4 −3.21−1.50 −2.4 8.3 E7 0.9 0.1 0.9 0.1 460.2 7088 2.6 −3.05 −5.06 −4.1 8.3 E81 0.8 0.2 467.9 5918 2.5 −2.73 0.43 −1.2 8.8 E9 0.9 0.1 0.8 0.2 462.86210 2.8 −3.9 −13.0 −8.5 9.0 E10 1 0.9 0.1 481.3 6863 3.0 −7.20 −5.73−6.5 7.4 E11 0.9 0.1 0.9 0.1 480.5 7090 3.0 −6.42 −8.84 −7.6 8.5 E12 10.8 0.2 482.7 5260 2.4 −3.92 −0.24 −2.1 6.6 E13 0.9 0.1 0.8 0.2 471.85036 2.3 −2.18 −2.62 −2.4 6.9 E14 0.7 0.3 0.7 0.3 460.4 2327 1.4 7.25−7.94 −0.35 6.8 E15 0.3 0.7 0.7 0.3 408.1 849 0.3 5.27* 2.58* 3.93* 6.4E16 0.3 0.7 0.5 0.5 414.3 6820 1.0 2.09* −3.11* −0.51* 8.2 E17 1 1 475.06672 2.5 −8.03 −6.22 −7.12 8.3 E18 0.9 0.1 1 468.6 3871 2.2 −0.23 1.450.61 8.0 *CTE values of CE7, E15 and E16 measured over 50-450° C. sinceT_(g)’s are less than 450° C.Polyimide/Copper-Clad Laminates

Four polyimide/copper-clad laminates (CCLs) were prepared by castingdifferent polyamic acid formulations (E1, E2, CE10 and E16) onto 12 μmCu foil (BHM-102F-HA-V2, JX Nippon Mining & Metals, Corp., Japan)followed by thermal imidization to form the CCLs using the followingprocedure.

PAA solutions were de-gassed for 10 minutes and then cast onto the matteside (silane treated side) of the Cu foils at 25° C. using a metal barto produce ˜1 mil dried films (the Cu foils had been adhered to glassplates prior to casting the solutions). The wet PAA/Cu-clad on the glasssubstrate was heated to 120° C. for 80 minutes on a hot plate exceptheated to 120° C. for 30 minutes for E16, resulting in a green film(65-70% solids)/Cu-clad multilayer. The multilayer on glass was thenplaced in a nitrogen-purged furnace and heated from room temperature to50° C. (1.25° C./min), followed by 50 to 400° C. (10° C./min) and heldat 400° C. for 5 minutes. The films were cooled from 400° C. to 50° C.over 60 minutes in N₂ protection and then allowed to cool to roomtemperature in air. The CCLs were removed from the glass and tested formechanical and electrical properties as shown in Table 2.

TABLE 2 Example E1 E2 CE10 E16 BHM copper μm 12 12 12 12 Dielectricthickness μm 23.6 19.3 27.0 27.0 Peel strength 90 deg, AR N/mm 0.12 0.130.25 0.24 Peel strength 90 deg, AS N/mm 0.13 0.13 0.23 0.28 D_(k), AR@10 GHz 4.46 4.34 3.75 3.82 D_(f), AR @10 GHz 0.0215 0.0276 0.01290.0133 D_(k), 23° C./50% @10 GHz 4.80 4.70 3.80 3.97 D_(f), 23° C./50%@10 GHz 0.0392 0.0426 0.0201 0.0191 D_(k), 85° C./85% @10 GHz 5.12 4.984.01 4.07 D_(f), 85° C./85% @10 GHz 0.0489 0.0506 0.0290 0.0242 CTE(MD), from clad ppm/° C. −3.73 −2.70 7.3 2.2 CTE (TD), from clad ppm/°C. 1.62 2.01 9.4 0.5 CTE (MD), from film ppm/° C. 0.50 1.9 −6.1 −9.7 CTE(TD), from film ppm/° C. −0.63 1.85 −1.8 −1.8 Modulus (film) GPa 9.6 8.67.8 8.2

Examples E19 and E20

For Examples 19 and 20 (E19 and E20), the compositions PMDA 1.0//DAPBI1.0 (E19) and PMDA 0.9/BPDA 0.1//DAPBI 1.0 (E20) were prepared followingthe procedure of E1, but varying the ratio of dianhydride to diaminewhile maintaining a solids content of 16 wt %. Table 3 shows the changein viscosity of the PAA solutions as the molar ratio of dianhydride todiamine is varied from 0.80:1 to 0.985:1.

TABLE 3 Viscosity after 1 hr Dianhydride: stirring Temp Example Diamine(Poise) (° C.) E19 0.80:1 19.20 24.0 0.85:1 24.32 24.7 0.90:1 62.72 26.50.95:1 302.1 33.0 0.95-0.97:1 300-500 27.0 0.97-0.985:1 2000-3000 27.0E20 0.80:1 19.20 24.4 0.85:1 23.04 24.9 0.901 58.85 27.0 0.95:1 392.533.9 0.95-0.97:1 300-500 27.0 0.97-0.985:1 2000-3000 27.0

By controlling the viscosity and solids content of PAA solutions orvanish forms used to form polyimide films, flexible films with highT_(g), low CTE and high tensile modulus could be readily made when thedianhydride to diamine monomer molar ratio was in a range of from 0.85:1to 0.99:1.

Note that not all of the activities described above in the generaldescription are required, that a portion of a specific activity may notbe required, and that further activities may be performed in addition tothose described. Still further, the order in which each of theactivities are listed are not necessarily the order in which they areperformed. After reading this specification, skilled artisans will becapable of determining what activities can be used for their specificneeds or desires.

In the foregoing specification, the invention has been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below. All features disclosed in this specification may bereplaced by alternative features serving the same, equivalent or similarpurpose. Accordingly, the specification and figures are to be regardedin an illustrative rather than a restrictive sense and all suchmodifications are intended to be included within the scope of theinvention.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims.

What is claimed is:
 1. A polyimide film comprising a polyimide derivedfrom a dianhydride and a diamine, wherein: the dianhydride comprisespyromellitic dianhydride; the diamine comprises a benzimidazole; themolar ratio of dianhydride to diamine that forms the polyimide is in arange of from 0.85:1 to 0.99:1; and the polyimide film has a Tg of 400°C. or higher, a tensile modulus of 6.0 GPa or more, and a coefficient ofthermal expansion of 15 ppm/° C. or less over a temperature range of 50to 500° C.
 2. The polyimide film of claim 1, wherein the dianhydridefurther comprises up to 70 mole percent of3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride, or a mixture thereof,based on the total dianhydride content of the polyimide.
 3. Thepolyimide film of claim 1, wherein the benzimidazole is selected fromthe group consisting of 5-amino-2-(4-aminophenyl)benzimidazole,5-amino-2-(3-aminophenyl)benzimidazole,6,6′-bis[2-(4-aminobenzene)benzimidazole],[2,2′-bi-1H-benzimidazole]-6,6′-diamine and mixtures thereof.
 4. Thepolyimide film of claim 1, wherein the diamine further comprises abenzoxazole.
 5. The polyimide film of claim 4, wherein the benzoxazoleis selected from the group consisting of5-amino-2-(4-aminophenyl)benzoxazole,2,2′-p-phenylenebis[5-aminobenzoxazole],[2,2′-bibenzoxazole]-5,5′-diamine, 2,6-(4,4′-aminophenyl)benzobisoxazoleand mixtures thereof.
 6. The polyimide film of claim 1, wherein thediamine further comprises up to 50 mole percent of p-phenylenediamine,m-phenylenediamine, m-tolidine, or a mixture thereof, based on the totaldiamine content of the polyimide.
 7. The polyimide film of claim 1,further comprising a crosslinking agent, a colorant, a matting agent,submicron particles or a mixture thereof.
 8. The polyimide film of claim1, wherein the polyimide film has a thickness in a range of from 4 to150 μm.
 9. An electronic device comprising the polyimide film ofclaim
 1. 10. The electronic device of claim 9, wherein the polyimidefilm is used in device components selected from the group consisting ofthin-film transistor substrates, substrates for color filter sheets,cover films and metal-clad laminates.